for the multimodal and cross-modal nature of the N400, on the assumption that the various meaning-laden stimulus types ultimately converge on shared (or at least partially overlapping) conceptual level representations. They can also easily explain both the sensitivity of N400 amplitude to pragmatic and discourse-level manipulations, and the relative precedence, in many cases, of such high-level factors over lower-level ones. However, a challenge for such late-stage accounts is the presence of N400s to stimuli that are not lexically represented in the mental lexicon (pseudowords and even illegal strings), and the emergence of N400 effects to lexically represented stimuli prior to their recognition point (i.e., before a listener knows which word s/he is hearing). Furthermore, for all of these stimulus types, N400 amplitude is sensitive to a whole host of factors whose sole or primary influence is presumed to be at earlier (pre-lexical or lexical) processing stages, such as orthographic neighborhood size and neighbor frequency, lexical (and subpart) frequency, orthographic and phonological similarity, and repetition. Finally, integration/unification processes have been linked to top-down control mechanisms, yet N400 effects have been observed under conditions in which such control seems unlikely, as for semantic priming effects under the attentional blink or repetition effects
